Dielectric tuning system



Sept. 16, 1952 R. L. HARVEY DIELECTRIC TUNING SYSTEM Filed June 30, 1948 INVENTOR EUBEBT LHARYEY ATTORNEY Patented Sept. 16 1952 DIELECTRIC TUNING SYSTEM Robert L. Harvey, Princeton, N. J., assignor to Radio Corporation of America, a. corporation of Delaware Application June 30, 1948, Serial No, $6,071

13 Glaims. 1

This invention relates generally to dielectric tuning systems and particularly to resonant circuits or-structures tunable over-an ultra high frequency range by a core having a high dielectric constant.

A number of frequencies within the ultra high frequency range from 100 to 1,000 megacycles (me) have recently been allocated to various commercial broadcasting services. Thus, frequency modulated carrier waves as well as black and white television may be broadcast within that frequency range; the frequencyrange from 480 to 920 me. has been tentatively allocated for experimental work relating to color television. It is therefore extremely important for the reception of modulated carrier waves that resonant circuits or structures aswell as oscillationgen erators be provided'which are tunable over a fairly wide ultra high frequency range.

In the past, resonant circuits comprising lumped capacitance and inductance have been tuned in various manners. In the radio broadcast held it is conventional practice to tune a receiver by a tuning condenser. More recently, resonant circuits have also been tuned by moving a ferromagnetic core relatively-to the inductance coil of the circuit'to vary the inductance of the circuit. However, permeability tuning can not be-used at frequencies of the order of 100 me. or more in view of the high losses caused by the ferromagnetic core. It is furthermore known that the frequency of a resonant circuit can be adjusted by eddy current tuning, in which case the inductance'of the resonant circuit is altered by moving a non-magnetic core of high conductivity with respect to the coil. Eddy current tuning inherently has high losses which become prohibitive at ultra high frequencies. Accordingly, none of these methods are feasible for tuning a resonantcircuit within an ultra high frequency range substantially above 100 me. In accordance with the present invention dielectric tuning is utilized where a core having a high dielectric constant is moved relatively to an inductance element or to a resonant structure having a distributed inductance and capacitance to change the capacitance of the resonant circuit. Dielectric tuning is particularly adapted for the ultra high frequency range.

vA resonant structure having distributed inductance andlumped capacitance, represented by'spaced plates, can be tuned by changin the capacitance as by moving a dielectric m r with respect to thespaced plates. Such a resonant. structure, however, has a low Q, wherev Q is the energy stored by the circuit divided by the energy lost per cycle of the resonant frequency of the circuit. Furthermore, the tuning range, of the circuit is limited because the resonant structure has an appreciable fixed minimum capacie tance, and only the additional capacitance provided by the movable dielectric member can be altered.

An oscillation generator developing a wave ofa frequencywhich is adjustable over an appreciable ultra high frequency range preferably should not have any sliding contacts since such. contacts are a source of erratic operation in ultra high frequency circuits. Furthermore, it: is desirable that the frequency of the wave developed. by the oscillation generator can be changed by asingle control. 4

It is the principal object of the present inventicn, therefore, to provide novel dielectric tuning systems suitable for use within an ultra high frequency' range.

A further object of the invention isv to provide an inductance element, or aresonant structure having distributed inductance and capacitance, which may be tuned over an appreciable ultra high frequency rangeby sliding within theinduct: ance element or'resonant structure a core hav-: ing a high dielectric constant.

Another object of the invention is to providean ultra high frequency oscillation generator tunable within a considerablefrequency rangev by a single control without utilizing sliding contacts.

In accordance with the present invention a dielectric tuning' system forultra'high frequencies comprises an inductance element such as a coil, particularly a strap wound coil, and a dielectric core. The core has a high dielectric constant which is preferably in excess of. 1,000 and is movable relatively to the coil to vary the resonant frequency of the coil. Movement of the core will alter or vary the distributed capacitancebetween the individual windings of the. coil and the dielectric core.

An ultra high frequency oscillatory circuit embodying the present invention may also comprise a resonant structure having distributed inductance and capacitance and a substantially uniform voltage distribution across its outer'surface. Such a structure preferably consists of a cylinder of conducting material slotted along its length. A dielectric core is movable with respect to the cylinder and preferably slides axially within the cylinder, Such an oscillatory circuit has a comparatively high Q and may beu'sed' with advantage in an ultra high frequency oscillation gen-' erator;

The novel features that are considered characwhen read in connection with the accompanying drawing, in which:

Fig. 1 is an elevational view of an ultra high frequency oscillation generator including a tunable resonant structure in accordance with the present invention;

Fig. 2 is a cross sectional view taken along line 2-2 of Fig. 1 and illustrating the resonant structure forming the oscillatory circuit and its dielectric core; v

Fig. 3 is the equivalent circuit diagram of the oscillation generator of Fig. 1;

Fig. 4 is a schematic view of a dielectric system embodying. th present; invention and includin an inductance coil; and

Fig. 5is a schematic view of a modified dielectric tuning system in accordance with the invention having a strap wound coil resonated by a dielectric core.

Referring now to Figs. 1 and 2 there is illustrated an ultra high frequency oscillation generatorin accordance with the present invention. The generator includes an oscillatory or resonant circuit consisting of resonant structure II) whichis a cylinder of conducting material having a slot I I. along its length. Dielectric core I 2 is arranged to move with respect to slotted cylinder I0. Dielectric core I2 consists .of. a material having a high dielectric constant which is preferably larger than 1,000. Certain strontium, barium or calcium titanates have dielectric constant of the order of 4,000. Such dielectric materials which have been disclosed, for example, in'the patents to Wainer 2,399,082, 2,436,839 and 2,402,518 are available with a power factor of less than 5 per cent corresponding to a loss of .05.

I Slottedcylinder I represents a resonant structuning ture having distributed inductance and capaci-,

tance. The inductance is substantially uniformly distributed, and the cylinder has a uniform voltage gradient across slot II so that the voltage is' distributed substantially uniformly along its surface. The frequency at which cylinder I9 resonates is determined by its dimensions, that is, by its diameter and length. When the diameterof cylinder I0 increases, its distributed inductance increases but, on the other hand, when its length increases, the inductance will decrease. Cylinder It! may be considered as a strap wound coil having a single turn.

Dielectric core I2 preferably fits closely within cylinder. I0 as illustrated in Fig. 2. It is to be understood that dielectric core I2 also will be resonant at a frequency which is determined by its dimensions or size. Core I2 should, of course, not be resonant within the frequency range to which the resonant circuit consisting of cylinder I0 may be tuned. However, the resonant frequency of core I2 may easily be changed by varying its size or its configuration.

Cylinder I0 is mounted by a suitable insulating material I3 on base plate I4 which bears gear rack I5. Shaft It is secured to dielectric core I2 and preferably consists of an insulating material. Pinion I1 is mounted on shaft I6 by bearing I8 and may be rotated by control knob 20 as shown schematically.- Ihus, when control knob 20 is rotated, pinion I'I engages with rack I5 anddielectriccore I2-may be moved into or out of cyl- 4 inder I 0. Thus, the distributed capacitance of resonant cylinder I0 may be altered, that is, when core I2 moves to the left into cylinder ID the distributed capacitance will increase, and the resonant frequency of the circuit will decrease.

The oscillatory circuit consisting of resonant cylinder I0 and dielectric core I2 may form part of an oscillation generator. The generator may include vacuum tube 2I which may be a triode of the 6F4 type, the base portion of which includes a plurality of contact prongs. Prongs 22, 23 are connected together as shown schematically, and make contact with the anode of the tube. Prongs 24 and 25 are also connected together as shown, and lead to the control grid of the tube. Prong 25 is connected to the cathode and prongs 21, 28 lead to the cathode filament.

. As shown in Fig. 1, prong 23 is connected to cylinder In adjacent slot II. On both sides of slot II cylinder ID has high impedance portions, that is, the voltage has an antinode. The diametrically opposite portion of cylinder II], that is, portion 30 (Fig. 2) has a voltage node to which a suitable voltage supply indicated by battery 3| may be connected through choke coil 32. Prong 24 is connected through capacitor 34 to the other high impedance portion of cylinder I 0. Thus, cylinder I0 is connected through prongs 23, 24 to the anode and control grid of triode 2 I. It will be observed that the connections to the anode and control grid can be made through very short leads which is very important in ultra high frequency work in view of the inductance represented by any lead.

Grid leak resistor 35 is connected between{ prongs 25 and 26, that is, between the controlgrid and cathode of the'tube. The cathode is grounded through resistor 36 while the filaments are energized by voltage source 3,! connected between prongs 21, 28. V

v The equivalent circuit of the oscillation generator of Figs. 1 and 2 is illustrated in Fig. 3. Res onant circuit 20 represents the resonant structure of cylinder I0. Forthe sake of illustration,

resonant-circuit .49 has been shown with lumped;

inductance element ll and lumped capacitor 42.

Dielectric core I2 is schematically represented,

One terminal of resonant circuit 40 is connected to anode i3 of triode 2| While the control grid M is connected to the other terminal of circuit 40 through coupling condenser 34. The ositive voltage supply indicated at +3 is connected through choke coil 32 to the midpoint of inductance ele{ ment 4| Control grid 44 is connected to cathode 45. through grid leak resistor 35. Cathode 45 is grounded through cathode resistor 36.

From an inspection of the circuit diagram of Fi 3 it will be obvious that the oscillation generatoris connected as a Hartley oscillator. Cathode 45 is connected tothe midpoint of 111- ductance element 4| through cathode resistor 36,

voltage supply +3 and choke coil 32. t1 0n of the oscillation generator will SEI'Y.

The generator of Figs. 1 and 2 operates best in I the frequency range between 500 to 1,000 me. It

will, however, operate at frequencies as low as me. and as high as 1,200 m'c., being limited at the high frequency end by the transit time of available tubes. The oscillation generator of Figs. 1

and 2 may have a tuning range of to 510 me with a cylinder I0 having an outer diameter of The operabe obvious and no further explanation is deemed to be neces- 5. tuning rangezhaswaratid of 3.2. Anotherembodi ment cf'th'e'oscillation generator-of Figs. land 2 had atuning range between 325'and'660 maceri'esponding to a tuning ratio of 2.04; In that case, cylinder lll had an outer diameter of 1"'and an inner diameter of /8 anda length of 1%". The length of coral: was the same as that of cylinder l and a clearance of .003" was provided between core 12 and cylinder 10. With different dimensions of cylinder I0, other tuning ranges can readily be obtained. If the oscillatory' circuit i0 is used as a wave meter or coupling element where the capacitanceloadingof tube 21 isabsent, a considerably larger tuning range can be obtained.

Fig. 4'illustrates another dielectric tuning sys-' tem in accordance with the present invention. Theultra high frequency tunable circuit compriseswire wound 001150. Dielectric core 52 may be moved relatively to core 50 as shown by arrows 53. Movement of dielectric core 52'in'to coil50 willincrease the distributed capacitance between the individual'windings of coil 59. Dielectric core 52 may be moved by strings 54 guided by pulleys 55, 56; Spring 51 is interposed between the free ends of strings 54 to provide proper-tension. Pulley-55 may berotated by control knob 58 which will control the resonant frequency of coil 50. Itwill be observed that a lumped capacitance i not needed and that coil 50 is resonated solely by its distributed capacitance.

The resonant circuit consisting of coil 50 may be resonated between 25 and 50 megacycles although the best working range is between 25 and 30 megacycles. 'By way of example, coil 50 may consist of 20 turns of .040 enameled wire while dielectric core 52 may have a diameter of .9 and a length of 1%". When dielectric core 52 is moved axially within coil 50, the tuning range of the circuit was 25.5 to 48.6 megacycles.

Fig. illustrates strap wound coil 60 within which dielectric core 6| may slide to alter the resonant frequency of the coil in accordance with the invention. Core Bl may be secured to threaded rod 62 which preferably consists of an insulating material. Rod 62 is supported by bearing 63 and may be rotated by handle 64 to move dielectric core 0! into and out of strap wound coil 60.

The capacitance change obtained when dielectric core Si moves relatively to strap wound coil 50 is larger than that which can be obtained in the circuit of Fig. 4. The tuning range of the resonant circuit is between approximtaely 50 and 80 megacycles.

There has thus been disclosed a dielectric tuning system for tuning a resonant circuit within an ultra high frequency range. The distributed capacitance of an inductance element such as a wire wound coil or a strap wound coil may be altered by means of a dielectric core. Alternatively, the resonant frequency of a resonant structure which may consist of a slotted cylinder having distributed inductance and capacitance may be changed by a dielectric core. Such a resonant structure has a large tuning range and a comparatively high Q and is suitable for the frequency range between 150 and 1200 megacycles. The resonant circuit or structure may be tuned by a single control and does not require sliding contacts. The resonant structure may form the oscillatory circuit of an oscillation generator.

What is claimed is:

1. A dielectric tuning system for ultra high frequencies comprising an inductance winding and a core consisting only of a material having a:high dielectric constant, Isaid core being movable relatively to said winding to alter the resonant frequency of said system by changing the amount of said material inserted within saidtinductance winding.

2. A dielectric tuning system for ultra high frequencies comprising an inductance coil and a .core consisting of a material having a dielec tric constant larger than 1,000, said core being movable relatively to said coil to change the resonant frequency'of said coil.

3. A dielectric tuning system for ultra high frequencies comprising a strap wound coil and a core having a high dielectric constant, said corebeing movable relatively to said coil to vary the resonant frequency of said coil.

4. A resonant circuit tunable within an ultra 5. An ultra high frequency tunable circuit comprising an elongatedresonant structure of conducting material slotted along its length and having. distributed inductance and capacitance, and a core consisting of a material having a high dielectric constant, said core being movable relatively to said structure to change the resonant frequency of said circuit by altering the quantity of said material in proximity with said structure.

6. An ultra high frequency tunable circuit comprising a resonant metallic structure having substantially uniformly distributed inductance and a substantially uniform voltage distribution along its outer surface, and a core consisting of a material having a dielectric constant larger than 1,000, said core being movable relatively to said structure to vary the resonant frequency of said structure.

'7. An ultra high frequency oscillatory circuit comprising a slotted cylinder of conducting material and a core having a high dielectric con-.- stant, said core being movable relatively to said cylinder to vary the resonant frequency of said circuit.

8. An ultra high frequency oscillatory circuit comprising a cylinder of conducting material slotted along its length and a core having a high dielectric constant, said core being movable relatively to said cylinder to vary the resonant frequency of said circuit.

9. An ultra high frequency oscillatory circuit comprising a cylinder of conducting material slotted along its length and a core having a dielectric constant in excess of 1,000, said core fitting closely within said cylinder and being movable axially within said cylinder to vary the resonant frequency of said circuit.

10. An ultra high frequency oscillation generator comprising a discharge device having a cathode, a control grid and an anode, an oscillatory circuit including a slotted cylinder of conducting material having two high impedance portions, one of said portions being connected to said anode, an impedance element for coupling the other one of said portions to said grid, a source of voltage connected between said cathode and said cylinder, and a core of high dielectric material movable with respect to said cylinder to vary the resonant frequency of said circuit.

11. An ultra high frequency oscillation generetcr comprising an electron discharge device having. a cathode, acontrol grid and an anode, an'oscillatcry circuit including a cylinder of conducting material slotted along its length and havingtwo high impedance portions, one of said portions being connected 'tosaid anode, a capacitor for coupling the other one of said portions to said grid, a source of voltage and an impedance element connected between said cathode and said cylinder, and a core of high dielectric material slidable within said cylinder to vary the resonant frequency of said circuit.

12. An ultra high frequency oscillation generatorcomprising a vacuum tube having a cathode, a control grid and an anode, an oscillatory circuit including a cylinder of conducting material slot,- tedalong its length and having two high impedance portions adjacent the slot, one of said portions being connected to said anode, a capacitor for coupling the other one of said portions" to said grid, a source of voltage including an impedance element connected serially between said cathode and the voltage node of said cylinder, and a core of high dielectric material slidable axially within said cylinder to vary the resonant frequency of said circuit. 7

13. A dielectric tuning system comprising in combination, an inductor having an appreciable surface area disposed essentially in the form of an .aipertured hollow c lindrical section and acylindrical core element of substantially the same dimensions as said cylindrical'section,flsaid-cor6 element having a high dielectric constant and being movable within said inductor to change the tuning of said system. 1

ROBERT L. HARVEY.

REFERENCES crrnn The following references are of record in the file of this patent:

UNITED STATES PA'I'ENIS Date OTHER REFERENCES ,War Department Technical Manual, TM 11- 1506, published Sept. 4, 1944; Fig. 184 on page 270, page 277; 2 pages of printed'znatter. 

